Remove outdated gcc_version checks.
Remove outdated gcc_version checks.

Follow-up to https://chromiumcodereview.appspot.com/13985038#msg4.

We do not support building with GCC 4.2 anymore, so those compiler tweaks
can be removed now.

R=thakis@chromium.org, abarth@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/13977026

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@149427 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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